Which statement is true regarding urination?

The statement that a lack of privacy and stress can affect urination is true because urination is not only a physical process but also one that can be influenced by psychological factors. Stress can lead to muscle tension and anxiety, which may cause difficulty in initiating urination or result in urgency. Moreover, the importance of privacy during the act of urination is significant for many individuals, particularly in institutional settings, as the presence of others can create discomfort that interferes with the normal urge to void. This highlights the connection between emotional well-being and the physiological function of the bladder, illustrating how environmental and psychological conditions impact urination.

The other statements do not accurately capture the complexities of urination in the context provided. Indwelling catheters can impact muscle tone due to reduced bladder usage, and while alcohol can lead to increased urine output, caffeine can stimulate urine production as well. Additionally, the bladder's capacity typically doesn't increase with age; in fact, it often decreases, leading to more frequent urination in older adults.